SpaceX return Dragon to space as Falcon 9 nails ASDS landing

SpaceX’s Dragon spacecraft returned to flight Friday with the CRS-8 resupply mission to the International Space Station: a mission which also carries a prototype inflatable module for the outpost. The first Dragon mission since a launch failure last June, Friday’s mission lifted off from Cape Canaveral at 16:43 EDT (20:43 UTC), followed by a historic first stage landing on the ASDS.CRS-8 Launch:

In addition to being Dragon’s return to flight, the CRS-8 launch is the first time it had flown in conjunction with the Falcon 9 “Full Thrust” version, which has replaced the Falcon 9 v1.1 that had been used previously.

Friday’s launch was the third flight of this configuration, which was previously used for December’s Orbcomm mission and the SES-9 launch in March. Overall it was the twenty-third flight of a Falcon 9.

The Full Thrust model is a further enhancement of the Falcon 9 design over the v1.1 – which was discontinued after the Jason launch.

The second stage of the vehicle has been stretched, the rocket’s engines have been uprated and the temperature at which liquid oxygen is stored has been decreased to around -207 degrees Celsius (55 Kelvin, -341 Fahrenheit), increasing its density and allowing more to be loaded into the tanks. Liquid oxygen is used to oxidise RP-1 propellant in both stages of the vehicle, producing the reaction which powers the vehicle.

These changes are geared towards increasing the rocket’s performance margins so that attempts to recover the first stage can be made on more missions, including flights to geostationary transfer orbits.

The final stages of Friday’s countdown began with a poll of flight controllers to determine readiness for fuelling operations thirty-eight minutes before launch.

With controllers go to proceed, loading of RP-1 propellant and liquid oxygen began three minutes later. Loading of liquid oxygen continued throughout the countdown to replenish the oxidiser as it boils off.

The last ten minutes of the countdown were an automated sequence during which the clock cannot be stopped without resetting to the start of the sequence. At the start of this period, chilldown of the rocket’s engines began.

Seven minutes before liftoff the spacecraft was placed onto internal power with the rocket also switching to internal power shortly afterwards.

Activation and arming of the flight termination system (FTS), explosive charges used to destroy the rocket should it go off course, took place three and a half minutes in advance of liftoff.

The US Air Force’s Range Control Officer and the Launch Director gave their final approval for launch on behalf of the Eastern Range and SpaceX respectively, two minutes and a minute and a half before the end of the countdown.

At the one-minute mark the rocket’s computers were commanded to begin their final preprogramed checks, the rocket’s propellant tanks were pressurised and the launch pad water deluge system, or “Niagara”, was armed and subsequently activated.

Three seconds before launch the flight computer sent a command to the first stage’s nine Merlin-1D engines to begin their ignition sequence.

Approximately a second later the engines, arranged in an octagonal or “OctaWeb” pattern, roared to life and begin building to full thrust.

The period between ignition and liftoff allows for an automated abort to be initiated should a problem be detected at startup. With no such abort is called the Falcon lifted off when the countdown reached zero.

Climbing East out over the Atlantic Ocean, the Falcon passed through the area of maximum dynamic pressure, or Max-Q, seventy-one seconds into flight. It achieved the speed of sound, Mach 1, at around the same time. First stage powered flight lasted two and a half minutes before first stage engine cutoff.

Stage separation occurred four seconds later with second stage ignition taking place after a further seven seconds. The second stage’s single Merlin Vacuum engine made one burn to attain Dragon’s target deployment orbit.

Following its separation, the first stage made three further burns; a boostback burn approximately four minutes into the mission put it on course for the Autonomous Spaceport Drone Ship and entry burn at around the seven-minute mark slowed the stage as it reenters Earth’s atmosphere.

With all going well the final burn resulted in a powered descent onto the landing barge.

While the first stage was attempting its landing, the second continued to burn as it accelerated Dragon towards orbital velocity.

Cutoff was around ten minutes after launch with separation of the Dragon spacecraft at around the ten-and-a-half-minute mark in the flight.

A minute and a half after separating from the Falcon 9, Dragon deployed its solar arrays.

For two days following launch, Dragon will make a series of engine burns to facilitate rendezvous with the International Space Station.

Upon arrival, Dragon will be captured by the station’s CanadArm2 robotic arm under the control of astronauts Tim Peake and Jeff Williams, and berthed at the nadir port of the Harmony module.

The pressurised cargo being delivered to the space station by CRS-8 comes to a total mass of 1,723 kilograms (3,799 lb).

This includes 640 kg (1411 lb) of scientific equipment, 547 kg (1,206 lb) of supplies and provisions for the crew, 108 kg (238 lb) of computer equipment, 12 kg (26 lb) of hardware to support EVAs using the US Extravehicular Mobility Unit (EMU) spacesuits, 306 kg (675 lb) of hardware for the US segment of the outpost and 33 kg (73 lb) for the Russian segment.

Other experiments being carried by Dragon include Rodent Research 3, which has been funded by Eli Lilly and Co and the Center for the Advancement of Science in Space (CASIS), to study the effects of spaceflight on the musculoskeletal structure of rodents in order to test drugs which could potentially help crews on future long-term missions.

The Microchannel Diffusion experiment will study how molecules of fluids behave at a microscopic level in microgravity as an analogue to how they would behave at an atomic level on Earth.

Following the arrival of the CRS-8 spacecraft at the International Space Station, BEAM will be extracted from the Trunk section by the station’s robotic arm and berthed at the aft port of the Tranquillity module; connecting to the space station via a Common Berthing Mechanism.

Following berthing, the module will be inflated to its full size; increasing from 2.16 metres to 4.01 metres (7.09 to 13.2 feet) in length and 2.36 to 3.23 metres (7.74 to 10.6 ft) in diameter. Expanded it will have a total volume of sixteen cubic metres (565 cubic feet).

Dragon is the only resupply craft designed to survive reentry into Earth’s atmosphere and be recovered, so it provides the ISS program with its only opportunities to return large items of cargo to Earth.

After hatches are closed, Dragon will be unberthed using CanadArm2 and released from the station. Following a series of separation burns it will be deorbited and the expendable trunk section jettisoned.

The pressurised module will reenter the atmosphere before descending under parachute for recovery in the Pacific Ocean off the coast of California.